Mineral matter characterization

Mineral matter characterization in coal has received considerable attention. Given and Yarzab (1) discussed the problems posed by mineral matter in various coal analyses. Furthermore, mineral matter complicates the chemical treatment of coal. It also has many adverse effects on commercial coal utilization. Coal consumers pay to ship mineral matter, to accommodate its impact on capital equipment and operations, and to dispose of the resultant ash. The impact of coal minerals on utilization motivated Consol s initial interest in mineralogy (2). The results reported here are from a second phase of the FTIR method development, in which extensive improvements were made to the methods. 

The types of mineral matter found In a particular deposit depend on the geography of the deposit. Those deposits found In the eastern part of the United States have mineral matter which Is rich In clay, quartz and pyrite. As a result utilities which burn eastern higher-sulfur coals must now use equipment which can reduce the sulfur oxides which are released. The deposits In the western parts of the U.S. frequently have mineral matter characterized by high calcite and sodium and lower clay and pyrite contents. The low sulfur content and some Inherent ability to capture liberated sulfur oxides with calcium compounds has led to the use of the low sulfur western coals for a growing part of the U.S. power generation market. 

Walker, P. L. Spackman, W. Given, P. H. Davis, A. Jenkins, R. G. Painter, P. C. "Characterization of Mineral Matter in Coals and Coal Liquefaction Residues", Annual Rept. AF-832 from Pennsylvania State University to Electric Power Research Institute, 1978. 

The above conclusions based on SEM-AIA measurements of association in terms of particle surfaces are somewhat more tentative than the conclusions drawn from bulk association distributions. There are more analytical difficulties when characterizing the particle surfaces than when characterizing the bulk sample. In addition, the factors determining the overall surface nature of a particle are more complex than just the relative amount of the phases present on the particle surface. However, the SEM-AIA results can still provide a useful and heretofore unavailable insight into the nature of mineral matter in coal. 

Inasmuch as mineral matter has been defined broadly to include all inorganic elements in coals, the chemical characterization of mineral matter involves the determination of many elements. In general, chemical analyses of geological materials have progressed from the wet chemical methods to sophisticated instrumental methods. The major elements in the mineral constituents of coal, Si, Al, Ti, Ca, Mg, Fe, P, S, Na, K, are the same as those in silicate rocks and are often determined by x-ray fluorescence spectroscopy and flame photometry. 

The two major problems encountered in investigating mineral matter in coal are that the mineral matter and coal are so intimately mixed that physical separation of the two is not feasible in a quantitative study and that the geochemical system is extremely complicated and difficult to characterize. The first problem is overcome in part by refining the tech-... 

Figure 17.12. Four components found by NMF in an oxisol obtained from a forest site in Western Kenya (J. Lehmann, unpublished data 2006, for site description see Kinyangi et al., 2006). (a) Mineral matter with low contents of organic carbon (b) organic carbon dominated by aliphatic and carboxylic forms (c) organic carbon dominated by aromatic forms (d) organic carbon dominated by carboxylic forms. Arrows in map (b) point to carbon features that share structures characterized by spectrum (b), and the feature at the horizontal arrow also contains aromatic carbon in contrast to the feature at vertical arrow.

Samples of raw and cleaned coals produced at the Ames Laboratory and obtained from TRW have been characterized for the mineral matter content and distribution among various particle sizes. The sulfur forms before and after treatment have been determined by conventional ASTM techniques and a direct SEM method. 

Given, P.H., et. al., Characterization of Mineral Matter in Coals and Coal Liquefaction Residues, EPRI Annual Report AF-832, Research Project 3361, Pennsylvania State University, December, 1978. 

Mineral matter. Guven and Lee (11) have performed a characterization of the mineral matter found in several deep-basin lignite seams. Using core samples from Shelby, Nacogdoches, Panola, and Rusk Counties in east Texas (Wilcox Group), mineral matter has been processed using low temperature ashing (LTA) procedures. 

Guven, H. Lee, L-J. "Characterization of Mineral Matter in East Texas Lignites" Texas Energy and Natural Resources Advisory Council, Report EDF-103, Austin, Texas, August, 1983. 

In the pyrolysis processes, a thermal degradation occurs between 400 and 600°C in the complete absence of oxygen. These processes are characterized by the indirect heating of the material through the furnace wall (or pipes). The pyrolitic products, the solid (mix of char metals and mineral matter) and the hot gases (condensable and noncondensable mixture), are collected. Their relative proportions depend on the nature of the material, the applied technology and the pyrolysis conditions, i.e. temperature, pressure, heating rate, etc. The reductive atmosphere of the furnace is mainly a function of the pyrolitic gas composition. 

This review (1) describes and classifies the geological, physical, and chemical occurrences of mineral matters in coal (2) summarizes analytical methods used to characterize the mineral matter and (3) compares the mineral-matter composition of Illinois coals with that of other U.S. coals. 

Characterization of the mineral matter in coal is important for a number of reasons. Because of the way coal must be mined, the mine-run product always includes some rock material other than coal, thereby contributing mineral matter to the mine product. Miners of a thin seam usually have to remove some roof and floor strata. Irregular bodies of roof shale or other rocks frequently occur within coal seams and inevitably become part of the mine product. Some coal seams grade upwards to shale coal or coaly shales so that there is no clear-cut boundary between coal and the roof rocks. In addition, many coal seams contain one or more mineral partings of various thickness so that miners must include these in the mine product. It is best for mining and sales purposes if the amounts, types, and characteristics of these rock materials be known prior to mining in order to properly design the mine and preparation plant. 

Chemical methods for the elemental characterization of mineral matter in coal have been extensively developed and reported. 

Clearly there is a need for improved techniques for predicting the behavior of mineral matter. This paper will provide a statement of the ash deposition problem in pulverized coal fired boilers it will present an assessment of the older, traditional methods for predicting mineral matter behavior and it will address some of the newer techniques that have been suggested as better ways of characterizing coal ash behavior. Additionally some areas of uncertainty will be identified which require the development of better predictive techniques. 

Coal beneficiation involves a series of steps to separate the mineral matter from the combustible portion of the coal. Current coal characterization for beneficiation is usually limited to measurements of the particle specific gravity distribution (washability). It is further assumed that the properties of the coal feed stream and related mineral matter remain constant during the separation or cleaning process, but the compositions of the streams do change. These changes are important in understanding the lack of expected separations. The effects of specific mineral constituents on different unit operations are described. Better measurement and analytical systems will permit improved control of the processes and better separations. 

The AIA-SEM technique has been used in Ames Laboratory to study the effect of grinding on the liberation of mineral matter from fine coal and its subsequent removal during cleaning. Several series of coals have been characterized by this technique in recent years, thus demonstrating its usefulness. In this work, the AIA-SEM technique was applied to determine the coal mineral character before and after cleaning by a float-sink technique. 

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